877
FXUS66 KPDT 252044
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
144 PM PDT Sat May 25 2024

.SHORT TERM...This afternoon through Monday night...Isolated
light showers will taper off over the Blue Mountains this
afternoon and evening, followed by mostly dry conditions as a
weak shortwave ridge moves overhead tonight through Monday
morning. Any light precipitation that develops overnight through
Sunday should remain pinned to the Washington Cascade crest as
orographic lift wrings some moisture out of the entrenched marine
layer.

Breezy to windy westerly winds have indeed materialized this
afternoon across climatologically windy regions such as the
Kittitas Valley, lower Columbia Basin of Oregon, eastern Columbia
River Gorge, and foothills of the Blue Mountains. While winds
reaching sustained advisory criteria are not anticipated (outside
of the Kittitas Valley), confidence is high (70-90% chance) that
limited portions of the eastern Columbia River Gorge, lower
Columbia Basin, and foothills of the Blue Mountains will see winds
of 25-35 mph with gusts of 40-45 mph this afternoon and evening.
In the Kittitas Valley, winds have been oscillating around
advisory criteria all morning and early afternoon, primarily with
respect to sustained winds (25-35 mph) as gusts above 45 mph have
been brief. Will maintain the Wind Advisory since rationale from
the morning update still appears valid -- in fact, cross-Cascade
pressure gradients have strengthened to 5-5.5 mb.

Sunday through Monday, mostly quiet weather, albeit with a
warming trend, is forecast. Winds will slacken compared to today
with just localized breeziness.

Monday evening into Monday night, as flow aloft turns
southwesterly ahead of an approaching offshore trough, guidance
is advertising a surge of moist, slightly unstable, mid-level air
into eastern Oregon and southeast Washington. While synoptic lift
appears weak, indicators for elevated instability and shower
development look good -- negative mid-level theta-e lapse rates
overlap an RH field in excess of 70% in the vicinity of the right
entrance region of a 300-200 mb jet. At minimum, expecting the
formation of an altocumulus field; at most, some isolated
thunderstorms may develop along with scattered rain showers
(10-20% chance). Plunkett/86

PREV DISCUSSION... /issued 926 AM PDT Sat May 25 2024/

MORNING UPDATE...The main update this morning was to increase
forecast wind speeds and gusts for the Kittitas Valley through
tonight. At the synoptic level, northwesterly flow through the
much of the column will persist over the PacNW as an upper-level
trough axis exits to the east over the Rockies through the day.
Moreover, morning soundings at SLE/UIL show the top of an upstream
marine layer around 850 to 750 mb. Cross-Cascade surface pressure
gradients range from 4-5 mb from SEA to ELN and are advertised by
CAMs to be maintained through the evening. While NBM and HREF
probabilities are marginally supportive of advisory criteria,
pattern recognition increases forecaster confidence. Thus, have
issued a Wind Advisory through 11 PM this evening as confidence is
high (70-80% chance) that marginal advisory criteria (sustained
winds of 25-35 mph with gusts of 35-45 mph) will be maintained
through the day. Plunkett/86

&&

.LONG TERM...Tuesday through Saturday...Models in good agreement
at the onset of the forecast period, with a system moving into
the PacNW Tuesday afternoon/evening. Moisture over the area will
produce light showers over the Blue Mountains ahead of this
arriving trough. As the trough axis advances over the west coast
on Tuesday afternoon, the Cascade Mountains will see an increasing
opportunity (40-70% chance) for high elevation showers. While most
will be rainfall, some mixed precipitation will be possible in
the cooler pockets.

The advancement of the trough across the forecast area on
Wednesday will continue the threat for high elevation
precipitation, with moisture also developing over the areas of
central Oregon. Confidence is not as significant with these
showers, with around a 10-20% chance of development on Wednesday
afternoon, decreasing through the evening. The departure of the
trough will bring a drier west to northwest flow across the area
late Wednesday. Through this point, models remain in generally
decent agreement, with cluster analysis demonstrating only minor
variations. Cooling temperatures noted with this set-up, with
values dropping 5-10 degrees between Tuesday and Wednesday. The
level to which these resultant temperatures drop below normal
overall mirrors their value drop (5-10 degrees below normal).

Models begin to diverge Thursday, with disagreements becoming
apparent in cluster analysis quickly. From the numerical guidance
perspective, there are two scenarios possible for the end of the
week. The first is a drier northwest flow persisting to keep
showers  generally at bay. The second is a trough and generally
northerly flow into Friday with some lingering moisture. The NBM
base of the forecast puts a lean on the slightly more active
scenario, with showers lingering over the high terrain. Regardless
of solution, a warming trend begins on Thursday.

By Friday, however, models come into better alignment with an
amplifying ridge. The degree of amplification does vary between
solutions, along with the pace of progression of the ridge through
the forecast area. The next system will advance in/towards the
PacNW on Saturday. The arrival time of the system again varies
with the pace of the departing ridge, with limited solutions
bringing precipitation into the forecast area. Current forecast
has a slight chance (10-20%) of showers over the higher peaks on
Saturday, with otherwise dry conditions and continued warming
temperatures. Branham/76

&&

.AVIATION...18z TAFs...VFR conditions through the TAF period with
dry conditions. The main impacts at area terminals will be gusty
to breezy wind through the evening. The strongest wind is expected
at KDLS and KPDT, where gusts of 30 to 35 kt are favored (85-90%
chance). Most other terminals will see the potential for gusts to
25 kts (70-90% chance). Wind will weaken between 03z and 10z
Sunday with winds generally below 12 kts expected through the
remainder of the TAF period. Branham/76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  71  45  78 /   0   0   0   0
ALW  44  73  49  81 /   0   0   0   0
PSC  46  76  51  83 /   0   0   0   0
YKM  40  73  43  79 /   0   0   0   0
HRI  44  76  48  82 /   0   0   0   0
ELN  43  68  44  76 /   0   0   0   0
RDM  33  72  40  79 /   0   0   0   0
LGD  36  69  43  78 /   0   0   0   0
GCD  35  71  43  81 /   0   0   0   0
DLS  46  74  49  79 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 11 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...86
LONG TERM....76
AVIATION...76